Tele Vue TV-NP101is OTA - Used

A 101mm Legacy: The Nagler-Petzval Design Refined

The NP101is represents the culmination of a design philosophy that Al Nagler began in 1980 with the 5" f/4 Multi-Purpose Telescope. Al took Petzval's portrait lens concept of widely spaced doublets and patented a fast telescope version to test eyepieces. Its fast, wide and flat field led through the 4" f/5.5 Renaissance, the fluorite-equipped 4" f/5 Genesis, the SDF and the Tele Vue-101 to the NP101, which reached virtually ideal color correction and improved field flatness. The "is" (Imaging System) version arrived in 2006 with larger rear elements and a larger focuser.

Tele Vue telescopes are built start to finish by a single technician in Chester, New York, with quality checks at several critical steps. Lens spacings are hand-tuned and each focuser is hand-fitted, which is how Tele Vue assures diffraction-limited performance, and every NP101is is tested there before it ships.

4-Element, f/5.4 Optics: 1.1 Arc-Second Resolution

The heart of the NP101is is its 4-element, two-group Nagler-Petzval objective. This design consists of an air-spaced doublet in the front cell and a larger-diameter doublet at the rear, and the larger rear doublet adds illumination at the edge of the field, which matters for large chips that are sensitive to light fall-off. The flat field is built into the objective, so no field flattener is needed for most cameras. The fully multi-coated optics deliver a visual resolution of 1.1 arc-seconds, allowing you to resolve fine detail on planets and separate tight double stars.

With a clear aperture of 101.6mm (4 inches), its aperture gain is 211 compared to a 7mm exit pupil. Combined with f/5.4, that light grasp brings out faint nebulosity and resolves the brighter globular and open clusters into stars. Tele Vue sums it up as an imaging and visual tour de force.

The 2.4" Imaging System Focuser: 10:1 Precision and 12 lb Payload

The NP101is uses a 2.4" rack-and-pinion focuser whose drawtube has a 3" entrance, so its 2.4" exit passes all the field rays leaving the rear elements; a larger focuser would add no illumination. The integrated Focusmate provides a 10:1 dual-speed reduction for critical focusing, while the drawtube is supported by a Teflon sleeve and secured by two adjustable tension screws and three lock screws. Each focuser is tested to hold 12 lb without flex; tighten the tension screws in unison to avoid focus shift.

The focuser's end-ring is designed for the Tele Vue Imaging System ("is"), allowing direct, threaded connections for cameras and accessories. The end ring is pre-set parallel to the focal plane, and if you see tilt in your images you can jack it with the supplied Allen keys and lock it with jam screws; a quarter turn of a jack screw moves 198 microns. For visual use, the indexed 2" Accessory Adapter carries a brass clamp ring, and its three thumb screws give enough holding power for the heaviest visual accessories.

A 25.5" Powder-Coated Tube and Hard Case

The NP101is optical tube measures 25.5" and is powder-coated aluminum. A captive sliding metal dew shield shades the objective, and a screw-on metal lens cover protects it in storage.

The front doublet attaches to the tube with three alignment screws that you should never touch. The custom hard-shell case (19 lbs with the telescope inside) has a lid that opens 180° and two removable accessory bags that must stay in place when carrying, as they hold the telescope down; the case is cut out for an optional Starbeam and Everbrite diagonal.

Supporting the 10.7 lb OTA: Mounting and Balancing

The tube is 4" in diameter and Tele Vue offers two ring options. The single ring (RS4-8004) is fine for visual and photographic use and is recommended with all Tele Vue alt-az mounts because it allows more balancing range. The dual ring set (MRS-4011) is best suited for critical photography and CCD imaging, with a central bar that varies ring spacing to fit a variety of mount heads and the BPL-1098 plate underneath for Tele Vue alt-az mounts.

On both systems you balance the tube by unlocking the bat handle screws, sliding the tube fore or aft and retightening. The bottoms carry 1/4-20 holes for mounting studs, and the accessory grooves take #10-32 screws for the Starbeam, Piggy-Cam and Sol-Searcher. For alt-az use, the Gibraltar-HD or Gibraltar5-HD are recommended for their sturdy legs, and Tele Vue makes adapter plates for popular German equatorial mounts.

Visual Astronomy: A 4.9° Maximum Field of View

The NP101is excels as a visual instrument, offering a magnification range from 10x to a recommended maximum of 250x. At its lowest power with a 2" 55mm Plössl or 41mm Panoptic eyepiece, it delivers a 4.9° true field at 9.8x or 13.2x, enough to frame the Andromeda Galaxy (M31) or sweep the star fields of the Milky Way.

In Tele Vue's words, the highly corrected wide, flat field and fast focal ratio put eyepieces to the test, which is why the NP line has long been Tele Vue's own eyepiece test bed. At higher power, the virtually ideal color correction shows Jupiter's cloud bands and the Cassini Division in Saturn's rings without a color fringe.

Imaging at f/5.4 and f/4.3 with 52mm Sensor Coverage

The "is" in NP101is stands for Imaging System, and this telescope is an astrophotographer's tool. At its native 540mm focal length and f/5.4 ratio, it produces a 5.3° image circle, and Tele Vue designed the focuser to light chips up to a 52mm diagonal. For even wider fields, the optional NPR-2073 0.8x reducer transforms the scope into a 432mm f/4.3 astrograph, capable of covering full-frame (43mm) sensors.

Imaging System accessories thread together from the focuser's imaging insert to the camera. For 35mm and larger formats, or any sensor with pixels under 6µm, use the LCL-1069 Large Field Corrector for the best edge sharpness, set 2.75" (69.85mm) from the camera sensor (2.67" for 53mm-diagonal sensors). With the NPR-2073, the back focus is 68mm for one-shot-color and DSLR cameras, or 50mm for full-frame monochrome with filters, and spacers that keep drawtube extension to about 0.75" (20mm) are recommended.

Sighting with the 540mm OTA: Pointing and Finding

The wide field of the NP101is makes it easier to locate objects than a long-focus telescope, but a reliable finder is still essential. Tele Vue particularly recommends the Starbeam reflex sight (SRT-2010), which attaches to the Ring Mount or Tube Rings and fits a cutout in the case. Remove it before any solar observing.

Alternatively, you can use the telescope itself as its own finder. By inserting a low-power, wide-field eyepiece like a 55mm Plössl, the NP101is operates at 10x magnification with a 4.9° field. That is wide enough to star-hop to bright deep-sky targets. For those who prefer a traditional finderscope, the Quick Release Universal Finder Bracket (QFM-1008) also attaches to the mounting rings.

Expanding the NP101is with the 2.4" Imaging System

Tele Vue designed its Imaging System accessories with each optical system, so they are matched to this telescope. Everything threads onto the included Imaging System Adapter, which replaces the 2" Accessory Adapter in the 2.4" drawtube.

• Reducers & Correctors: The NPR-2073 0.8x Reducer provides a wider, faster f/4.3 system, while the LCL-1069 Large Field Corrector optimizes edge performance on 35mm and larger formats and on cameras with pixels under 6µm.
• Camera Adapters: Tele Vue offers a range of threaded adapters, including standard T-rings (TRG-1072), wide T-adapters for Canon (CWT-2070) and Nikon (NWT-2073), and an M54 adapter (M54-1073) for full-frame cameras and filter wheels.
• Spacers: The TLS-2245 set holds all six spacer rings (0.25", 0.375", 0.5", 1.0" threaded, plus 0.040" and 0.080" rings that fit between them), in black anodized aluminum with anti-reflection threads. The AFT-1105 adapter takes 48mm filters and adds 0.25" of spacing.
• Magnifiers: The 2x (PMT-2200) and 4x (PMT-4201) Powermates are recommended, used with the 2" Accessory Adapter, the matching T-ring adapter (PTR-2200 or PTR-4201) and the 3.5" extension tube.

NP101is vs. the TV-85 and NP127is: Choosing Your Tele Vue

The NP101is sits in a strategic position within the Tele Vue lineup, balancing aperture, portability, and field of view. Understanding its siblings helps clarify where it excels.

• vs. Tele Vue-85: The TV-85 is significantly more portable, with a 600mm f/7 doublet objective. Tele Vue pitches it as small enough for an airline carry-on. The NP101is has about 43% more light-gathering area, a faster f/5.4 focal ratio and a flat field for imaging, at the cost of more size and weight.
• vs. Tele Vue-NP127is: The NP127is is the larger sibling, boasting a 127mm Nagler-Petzval objective. It gathers 58% more light than the NP101is and has a slightly faster f/5.2 focal ratio. While visually more powerful, the NP127is is a heavier and longer instrument (14.5 lbs), requiring a more substantial mount. The NP101is gives you the same imaging system in a lighter 10.7 lb tube.

A Note on Used Condition

This Tele Vue TV-NP101is is a used telescope in good condition, sold as a complete imaging package. Along with the optical tube, it comes with a Tele Vue Qwik Point finder, both matching Tele Vue correctors (the NPR-2073 0.8x reducer and the LCL-1069 Large Field Corrector), a Feather Touch Focus Boss II controller with hand control and HSM focus motor, a Tele Vue Imaging System adapter kit with T-ring adapter, spacers and shims, tube rings, a dovetail plate and a hard case. This used telescope is sold without warranty. It is a single unit: once it is sold, it is gone.